Coating composition containing nitrocellulose



Feb. l0, 1931. A. w. BuRwr-:LL

COATING COMPOSITION CONTAINING NITROCELLULOSE Original Filed Dec. 20,1926 Vacaum Pump Patented Feb. 1o, 1931 UNITED STATES PA/TENT OFFICEARTHUR w. BUBWIIL, OI' N IAGABA FALLS, NEW YORK, ASBIGNOB TO ALOXCHEHICAL CORPORATION, 0F NEW YORK, N. A CORPORATION OF NEW YORK yCOATING COIYPOSITION ('20'.N'IFAIININGI NITBOCELLULOSE Originalapplication lied December 20, 1928, Serial No.` 158,058, and in GreatBritain October 6, 1927. Divided and this application illed January 12,1928. Serial No. 246,097.

This invention relates to products partielllarly adapted for use incoating compositions containing nitro-cellulose, to the process ofmaking the same, and to compositions, particularly artificial .leathercompositions, containing these products.

The present application is a division of my application Ser. No.156,053, filed December 20, 1926. l

In the preparation of artificial leather compositions, it is customaryto spread upon the fabric base a coating composition comprising asolution of nitro-cellulose in ethyl acetate, butyl acetate or othersuitable solvent, together with diluents such as, for example, benzol,alcohol, gasoline or the like, pigments and other fillers, and an oil oroils of the nature of castor oil. The benzol, alcohol, and gasoline areused as diluents as they alone are not solvents for nitro-cellulose. Theoil cal characteristics of, the nitro-cellulose whereby the dry coating,obtained upon evaporation of the volatile solvents and diluents,

remains soft and iexible.

The relatively high cost of castor oil precludes the use of thissoftening agent in many instances, and substitutes therefor have beensought. For example, it has been attempted to substitute for castor oilthe so-called artificial leather compositions.

I have found that, by the liquid-phase oxidation, under controlledconditions, of hydrocarbons or mixtures thereof such as those occurringin petroleum oils, there may be obtained organic carboxylic acidproducts from wlnch a valuable softening agent may be obtamed, whichsoftening agent is equal, and 1n many cases superior, to castor oil inoating composltions containing nitro-celluose. f Y

More particularly, the present invention concerns the. saponifiablecarboxylic acid products obtained by the controlled oxidation ofmid-continent or Pennsylvania petroleum dlstillates having a density offrom about to 40 Baum, although I have found that these acid productsare obtainable from other petroleum distillates than those justmentioned.

The process of making these saponiable carboxyllc acid products consistsgenerally in y the liquid-phase oxidationof hydrocarbons or mixturesthereof, including both light and heavy petroleum distillates, undersuch conditions as to limit the formation vof compounds insoluble inthepartially oxidized mass and the isolation of the acid bodies from thepartially oxidized mass.

Although this invention is not restricted to use of any particularhydrocarbon or mixture of hydrocarbons, I prefer to use asstartingmateiial petroleum distillates having densities of approximatelyL18"-13 Baum at 16 C. Especially suitable-is the 45 Baume distillateknown as kerosene. This particular petroleum fraction has a distillationrange substantially as follows:

When a petroleum distillate of the above soluble in the petroleumdistillate, with ory without the presence of water-soluble carboxylicacids of relatively low molecular wei ht. The water-insoluble carboxylicacid bodies may be removed from the solution by various methods, as forexample, by treating the solution comprising the said acid bodies andunoxidized petroleum distillate with an aqieous solution of an alkali,thus forming al ali metal soaps of the said acids, separating the soapsfrom the unoxidized material, decomposin the soaps by treatment with asuitable aci and isolating the thus purified and liberated acids.

The invention will be described and illustrated hereinafter by referenceto a batch process. It is to be understood, however, that the proceduremay be made continuous, as shall be explained.

In the accompanying drawing there is shown diagrammatically one form ofapparatus suitable for us in carrying out the process of the invention.l y

The oxidation step proper takes lace in an upright cylindrical reaction'vesse or oxidizer 1, which may be, for example, about 5 feet in diameterand about 16 to 18 feet in height. The oxidizer 1 may be made of anysuitable material such as iron or steel and should be capable ofwithstanding pressures nlp to 350 pounds per square inch. Prefer a lythe oxidizer 1 should be made of or iine with material which isresistant to the corrosive action of the reaction mixture; for example,provided with an inner shell of aluminum 2. The oxidizer is provided ata point near its lower end with a tight coil 3 which serves as a heatingor cooling coil as required. Suitable means, not illustrated, such as' ajacket surrounding the oxidizer, also may be used to control thetemperature of the oxidation reaction. At a point between the lower endof the oxidizer 1 and the tight-.coil 3 is an air spray pipe 4 connecteby pipe line 5to an air compreor 6. Air s ray pipe 4 is so designed thatair is ejecteld from -it in the form of fine bubbles.

7, 8 and 9 are a valved hydrocarbon' supply pi e, a valved liquiddischarge pipe an va ved gas discharge pipe, respectively. 10 is apressure gauge, and 11 is a thermometer. 12 is a separating tank fed by'the valved liquid discharge pipe 8 leading from the oxidizer 1; saidtank being provided with agitating means (not shown From the bottom ofthe separating tank 12 extend the valved conduits 13 and 13 for thetransference of fluids to the 'acid precipitating tank 17 and to thepetroleum distillate supply tank 14, respective1y. AThe -tank 17 may beof any suitable material (e. g.of lead) adapted to withstand thecorrosive action of strong acids.' 15 and 16 are valved supply ipes forconducting water and sodium yroxide solutions respectively to the serating tank 12. 18 is a valved supply pipe for conducting sulfuric acidto the tank 7. The valved dischar e line 19 leads to waste and thevalved disc arge line 19 leads to the still 20 which is provided withthe valved discharge conduit 21. 22'is a condenser, 23 is a distillatereceiver and 24 is a vacuum pump.

The process is carried out in the apparatus illustrated as follows:

A petroleum hydrocarbon oil, such as, for example, the Baume distillateabove described, is charged into oxidizer 1', a small amount of anoxidizing catalyst or exciter of oxidation such as a compound ofmanganese copper or iron, say manganese oleate, amounting to about 0.1percent of the weight of the oil is added and the mixture heated u to atemperature in the neighborhood of C. or higher, referably to about13b-140 C., and an oxi izin gas, preferably air, is supplied throught es ray pi 4. are permitted to accum te in t e oxidizer until the desiredpressure is reached, after whichthe pressure is maintained or regulatedb controllin the discharge of gases throng the valve gas discharge ipipe9. The pres. sure may vary considerab sa from 150 to 350 pounds lpersquare inc e preferred ressure wi depend upon a number of contionsincludin the tem ture main--A tained, the kind di hydrocar n mixtureunder treatment, the rate of .air supply and,- if oxygen-enriched air isused, upon the ricliness of the oxygen supply. It is preferred to carout the oxidation rocess under such con 'tions that the reaction issubstantially i self-sustaining. 'In general, the reaction isself-sustaining ata temperature of about 135140 C., and at'a pressure ofabout 250* i ounds per square inch, with the. hydrocaron undertreatment, although temperatures and pressures may vary between widelimits. Thus, for example, oxidation has been ob served at a temperatureas low as 100 C.; -it

is more ra id above 120 C., and the temperature may allowed to rise to155 C..with satisfacto results under some ciruma stances. herefore,while I prefer to carry out the oxidation process at a temperature atwhich the reaction rate is fairly rapid, say 135-140 C., it is to beunderstood that the invention includes the employment of -all suitabletemperatures at which oxidation takes place.

During the oxidizing treatment, as is stated above collect in the u rend of oxidizer 1 are rele thro hp e pipe'9.

These gases contain practi y no oxygen but do contain carbon dioxide,nitrogen an va uantities of volatile acids ketones ntq volatile acids,ketonesA and-other products may be condensed in a suitable condenser(not shown) andA further treatedv for the recovery of formic acid, mixedlight ketones, etc. A

During the course of the treatment of the petroleum distillate in theoxidizer 1, there appear to be formed, during the earliest stages ofoxidation, f ormic acid and hi h mo ecular. weight ketonic and/or aldehy'c bodies; continued oxidation results in the production of saponifiablecarboxylic acids soluble in the petroleum hydrocarbons and havingmolecular weightsl approximately one and one-half times those whichwould naturally be calculated for acids derived from the original (i.e., unoxidized) hydrocarbons. Prolonged oxidation convertsthesepetroleum-soluble carboxylic acids into petroleuminsolublehydroxy-carboxylic acids having about the same molecular weights asthose which would naturally be calculated for acids derived from theoriginal hydrocarbons, low molecular-weight ketonic and/or aldehydicbodies, and additional amounts of formic acid. For the purposes of thepresent invention it is desirable to continue the oxidation treatmentuntil the maximum amount of the saponifiable, high molecular-weight,carboxylic acids soluble in the petroleum hydrocarbons has beenvobtained while avoiding the formation of petroleum-insolublehydroxy-carboxylic acids. The .formation'of the latter-named compoundsdepends upon several factors, principally the presence, or absence, inthe starting material, of crystallizable bodies (e. g., wax) andhydrocarbon compounds having a high molecular weight. That is to say,the higher the percentage of non-crystallizable bodies composinlg thestarting material (i. e., petroleum ydrocarbon mixtures), and the lowerthe molecular weights of these bodies, the more prono this startingmaterial-is to form petroleuminsoluble hydroxy-carboxylic acids, andvice Versa. Therefore, in the present instance, the oxidation o f 45Baum petroleum distillate (i. e., kerosene) should be carried only toabout 20% complete oxidation. The preferred degree of oxidation may becontrolled by titration, or by observing the incipient formation of thepetroleum-insoluble bodies.

The oily mixture obtained according to the above procedure is removedfrom the oxidizer 1 through the valved liquid dischargle pipe 8 into theseparating tank 12, and was ed with water. This washing operation hasIfor its purpose the removal of Water-soluble bodies. After thewithdrawal of the Wash water, sufficient dilute caustic soda isintroduced, through the valved supply pipe 16, to exactly neutralize thewater-insoluble acids present in the oily mixture and the mixture is umsoaps of t e carboxylic acids. After the soap solution has settled tosome extent a test 1s made to determine whether or not the aqueous soapsolution is of such a high concentration as to hold,perha s in colloidalsolution or sus nsion,-any o the unsaponied oils. In t` e event that thesaid soap solation is of such concentration, it is suiciently dilutedwith water introduced, for example, through valved suppl pipe 15, tocause the se aration of the sai unsaponified oils: The w ole mass isthen allowed to settle until both the oil and the soap solution areclear. The se arated soap solution is drawn oi, through t e valvedconduit 13, into the acid precipitating tank 17.

The su ernatant unsaponiied oil, consisting usual y of from 68-80% ofthe total mass, 1s drawn off, through the valved conduit 13', to thepetroleum distillate supply tank 14 for admixture with additionalquantities of fresh distillate', and is again subJected to' theoxidizing treatment in the oxidizer 1. It is a fact worthy of noticethat the petroleum h drocarbon mixture comprising in part t e .materialwhich has already been sub]ected to treatment does not require theresence of an oxidizing catalyst or exciter o oxidation to effect normaloxidation, the oxidation proceedmg in a manner identical to thatobservable upon oxidizing a fresh charge of the startmg'materialcontaining an added exciter of odixation.

The clear soap solution in the acid precipi-` tating tank 17 isdecomposed by treatment with a suiiicient amount of a suitable acid, forexample sulfuric acid, in a manner substantially as follows: Into thesoap solution, agitated by any suitable means (for instance, by a streamof air), there is introduced gradually, through the valved Supply pipe18, an amount of sulfuric ald sufficient to decompose all ofthe soap, orslightly in excess of that amount. vThe completion of this operation maybe determined by observation, or by the use of Congo paper or othersimilar means of testing. When testing for the completion of thedecomposition with Congo paper, the reaction should not be considered'complete at the first indication of color change in the test paper, butthe addition of acid should be continued until the color change is verystrong. By following this procedure the soap is completely decomposedwith the production of an oily mixture containin purified freewater-insoluble carboxylic acids, an aqueous vsolution containing sodiumsulfate. The slight excess of sulfuric acid referred to serves topromote a clean separation. lAfter settling, the contents of the acidprecipitating tank 17 is found to comprise two well-separated layers;the one comprising the oily mixture containing purified water-insolublecarboxylic acids having a specic gravity beagitated, formin thereby asolution of soer products of the oxidation. The di tween .945 and 1.0,and the other oomprisn `an aqueous solution containing sodium su fate.The latter solution is discharged 'through the valved discharge line19'.

5 'lhe oily mixture thus obtained contains some volatile bodies whichmight depreciate the value of theproduct as a softening agent fornitrocellulose compositions, if allowed to remain therein, consequentlyit is prefer-y able to remove such volatile bodies. As one manner inwhichthis operation may be effected, I prefer to subject theoily mixtureto vacuum distillation and to a treatment with steam substantially asfollows:

The oily mixture is withdrawn from the acid precipitating tank 17,through the valved discharge line 19, into a still wherein it isdistilled at a temperature not exceeding about 150 C., under a iessureof 20 from 10-20 mm. 'of mercury, an in an atmosphere of superheatedsteam, air or other suitable in'ert gas.

Under the above conditions, the said volatile bodies contained in theoily mixture are l2&5 volatilized and carried out of the still 20 un-(i. e., sweetening) is conducted, the specific gravity of the purifiedproduct obtained from 45 Baume fuel distillate will be found to bebetween 1.0110 and 1.0150.

The vacuum distillation and subsequent steam treatment should beconducted under such conditions as not to allow over-heating of thecarboxylic acids, since temperatures of about 160 to 175 C. apparentlycause some undesirable polymerization and/or decomposition. In general,it may be stated y that the lower the temperature to which the oilymixture is raised for the complete removal of all bodies which, at roomtemperature or somewhat higher, will volatiliz'e over a long period oftime (e; g., a year or more), the better the grade of softening agentproduced. Also, it is to be noted that the higher the viscosity of thefinished product the better, for the reason that larger proportions ofthe softening agent may be admixed with the nitro-cellulose'.

In preparing nitro-cellulose coating coinpositions containing theabove-described softening agent, I have found that the latter may beintroduced in amounts up to 95% of the total composition withoutdetriment, although I prefer to incorporate about 7 0-80% of thesoftening agent with labout -15% 05 of nitro-cellulose and about 5% ofpigments 'a secondary carbon atom in the'hydrocarbon and filler,dependin upon the dered relative softness or sti ness of the com ition.'l `h e economic advantage in the use o compositioiis containing theserelatively high propprtions of softenin agent is especially obvious whenit is considered that the softening agent is considerably less ex nsivethan eitherthe castor oil or the mtro-oellulose. Also, i t is known thatordinary castor oil can not be introduced into the nitro-cellulosecoating composition in an amount exceeding about of the totalcomposition without detrimental sweating or separation. The ability toblend with very small proportions of nitro-cellulose to the productionof stable, non-separating dispersions characterizes this softening agentin contra-distinction to castor oil or the so-called blown oils.

Another characteristic vof the new carboxylic acids comprising theabove-described softening agent is that t ey may be esteriiied, by anyof the methods commonl practiced for esterifying fatty acids genera y,thereby producing esters having properties very similar to castor oiland adaptable -for use as a substitute for castor oil in numerousrelations. Y

While the above-described procedure for preparin the softening agent hasbeen set out as a .atch process, it is to beunderstood that theinvention is not restricted thereto, and that the process may be made acontinuous or cychc rocess withn obvious economic advantages. orexample, a body of distillate may be subjected to controlled -partialoxidation while moving through the oxidizer, the reaction mixturecontainm petroleumsoluble carboxylic Aacids may contacted with,..forinstance blown in the form of a spray into, a solution of a causticalkali, the reaction mixture continuously transferred to a. separatingtank from which unoxidized. oil and soap solution may be separatelyremoved, the unoxidized oil continuously removed from the separatingtank and returned 11o to the body of distillate, and the soap solue tiondecom osed and the resulting freecarboxylic aci s purified in theregular manner.

While the production of the hereinbefore described softening agent isnot restricted to any particular theory of oxidation reactions, thefollowing is advanced as being a probable explanation of said reactions:

In regard to the reactions which may take place during the controlledoxidation of petroleum hydrocarbon mixtures by means of air underpressure at reacting temperatures, it is thpug t; that the mainprimaryreaction is one in which the oxygen attaches itself to ico chain and, ingeneral, it is believed that the rst secondary carbon atom after theprimary carbon atom,-in other wordsl the car-y bon atom in the -positionto the CH, group at the end of any chain or branch,is the one 130`higher molecular weight and the group lower molecular` weight isoxidized to the to .which the oxygen first attaches itself;- It isfurther the opinion, from many observations, that the oxygen is absorbedwithout the loss of any hydrogen; in other words, a

hydroxyl group is formed at this point, thus lieved that this is due tothe end hydrocarbon radical being eliminated in the form of formic acidb the oxidation of a `ketone formed from t e secondary alcohol in which15 the hydroxyl is attached to the carbon atom.

The above conclusion is supported by the fact that when a secondaryalcohol is oxidized it first forms a ketone. When a ketone which is amethyl X ketone,-that is, one in which the methyl group is on onesidexof the CO group and a roup of very much ln' her molecular yveig tis on the other side o the O group,-such ketone 'oxidizes in such manneras to leave the CO oup attached to the larger molecule, the 0 group thusbecoming the carboxylic group of the high molecular weight acids and theCH,i group forming formic acid. .The rule in other words is that whenketones are oxidized the CO group-attaches itself to the radical o;

corresponding acid containing only the total number of carbon atomswhich t at group has minus the C() group.

This view is furthersup ortedrby the factthat of the oil remainin a rremoval of all easily volatile and al acid products the greaterproportion forms crystalline compounds with bisulphite, indicatingithepresence of rather large amounts of etones or aldehydes but, as beforestated, the opinion linclines to the formation of ketones rather thanaldehydes because of the very large production of formic acid. When itis considered that one is treating hydrocarbons with an averagecomposition around CMH and that one obtains as high as 15% of actualformic acid there seems to be almost no other explanation for the mainor principal reaction.

It has also been found that the mixture ofl acids produced underconditions tending to avoid production of hydroxy acids shows amolecular weight which, in most cases, corresponds to hydrocarbons ofabout 50% higher molecular weight than those chosen for the oxidation.This may be accounted for in two possible ways. There may be incipientoxidation in the end hydrocarbons,that is, of the lmethyl group of thehydrocarbons,in such a way as to eEect what is known as the Kolbereaction. If simultaneously, by an atom of oxygen, two hydrocarbonmolecules are `so oxidized that the methyl group, in the ,able thatthere4 would be a synthesis o case of each molecule, loses one hydrogenatom we would have a synthesis immediately of the two hydrocarbonmolecules forming one of twice the molecular weight less two hydrogenatoms. The other possible explanation, which would appear to be thestronger,

is as follows: The acids -when firstv formed are extremely liable tofurther oxidation and as in ractically all cases one would have at theot er end of a straight chain, or at any other branch, a carbon atom inrelatively the same position as the first secondary carbon atom whichhad been oxidized to ketone and acid which also would be oxidized,probably almost simultaneously to an alcohol. acid in one `casewouldeither form a lactone with itself or would form an ester with thealcohol at the other end of the same chain in another molecule of thesame or other acid,

The i those of higher molecular weight, it is probthis kind producing anaverage molecularl weight of about 50% higher value than the simpleacid.theory would account for.

It seems proper to infer, from `the above theory, that the oxidationreactions occur in such manner that very large molecules are formed bythe esterification of hydroxy-acids by acids of the same, or higher, orlower, molecular wei ht, thus forming almost endless chains.Sgeparations by partial precipitation have obtained from acids whichvshow an average molecular weight of about 360, acids having molecularweights as high as 800 and, from the same mixture there have beenprecipitated acids having molecular weights as low as 100.A This isparticularly true where the oxidation has been carried far enough toform petroleum-insoluble hydroxycarboxylic acids. This would verynaturally be the case since it is just'these acids which one knowsare-the hydroxy-acids'as they show a considerable absorption of acetyland lwe' have now proof` of their polymerization either throughesterization or through polymerization due to the fact that they havethe hydroxy-group. This hydroxy group also may readily become a ketonegroup, as isreadily perceivable. Ketones in themselves are alsoextremely active; especially, the higher ketones show a great tendencyto polymerize. This may be an added cause for the-production of acids ofextremely high molecular weight.

An additional fact which supports the idea of ester acids or ketoneacids being formed is that if these higher molecular weight acids laredistilled without too much destruction,

of lower molecular-weight than those put in lthe still and ketonesf notvery high 4molecing assenti ular weight. This would -apl ar to su ort ltliester acids hypothesis. pe l PP laim.

1 A coatin composition comprising-'5&5

parts by weg tof nitro-cellulose and 50-95 parts by weilhtof a softeningagent consisty of the water-insoluble, saturated aliphatic, highmolecular-wei`ght,` carboxylic acid product obtainable by contacting `afree-,oxygen-containing gas with a petroleum hydrocarbon mixture in liuid state, in

the presence of an exciter of oxidation, at a reactive temperature above100 C. and not substantially above about 155 C. and `at a pressuregreater than atmospheric pressure ut substantially not above about 350pounds p01` Square inch, to the point of incipient formation ofpetroleum-insoluble bodies in said mixture. l e

i 2.-A coatin composition comprising 50-5 parts by weig t ofnitro-cellulose and 50-95 parts by weilht of a softening agentconsisting essentia yof the water-msoluble, saturated aliphatic,boxylic. acid product obtainable by contact# ing a free-oxygencontaininggas with a petroleum hydrocarbon mixture consistin of a 48-43 Baumpetroleum distillate in' 'quid state, in the presence of an exciter ofoxidation, at a reactive tem rature above 4'100 C. and not substantia yabove about ressure greater than atmosut substantially not above 155 C.and at a pheric pressure about 350 pounds per square inch, to the int ofincipient formation of petroleuminso uble bodiesm said mixture. 4

3. A coating composition suitable for use in the production o prisingnitro-cellulose and a softening agent consistm essentially of theAwater-insoluble, saturate aliphatic, high molecular weight,

carboxylic acid product obtainable by contacting afree-oxygen-con'taininggas with a petroleum hydrocarbonmixture consistinof a 48-43 Baum petroleum'distillate in iquid.s tate, in the presence ofan exciter of oxidation, at `a reactive tem rature above 100 C. butsubstantially not a ve about 155 C. and at a pressure i pressure butsubstantially not above about 350 pounds per square inch, to the pointof incipient formation of petroleum-insoluble bodies in said mixture. Intestimon whereof, I aix my si ature.

THUR W. BUBl LL.

high molecular weight, car-V artiicial leather, -com ater thanatmospheric

